ATP and 2,3-diphosphoglycerate (DPG) binding in cold-stored human erythrocytes will be evaluated with 31P nuclear magnetic resonance spectroscopy. The percent organic phosphate bound within intact cells at 5 degrees C will be assessed by comparing the change in chemical shift (Delta delta) of ATP and DPG observed in intact erythrocytes with the corresponding Delta deltas determined in model systems, and relating this ratio directly to the binding ratio. Binding in the model solution will be determined by membrane ultrafiltration. Another study which will be pursued is the question of whether ATP may be bound through both phosphate and nonphosphate groups under various conditions, e.g. with model solutions of pH 7.2 and 6.75 and at 37 degrees and 5 degrees C. This investigation will require comparison of percent binding with Delta delta values in hemoglobin solutions containing various ATP concentrations.